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Overview

Soekris sells mounting kits for 2.5" hard drives, which include a mounting bracket, standoffs and a short signal cable. net4801 supports PATA. net5501 supports PATA or SATA (this is connected by a bridge to PATA; you can't use both ports and a CF; it is possible to use one PATA and one SATA drive together with a workaround). For DMA support on net5501, use comBIOS 1.32i or newer, and a recent OS release.

Duty Cycle Considerations

If you're going to run 24*7, then you probably want to be running a drive designed for that purpose. Most laptop drives spend much of their lives either switched off or spun down to save the laptop battery and are not rated for continuous operation. Ordinary laptop drives may fail prematurely if you use them for a server application.

If you'd like to purchase a high duty cycle drive, it might be necessary to look for a storage specialist; they are often not carried by general-purpose PC hardware suppliers.

Block Size Considerations

Historically block size has been fixed at 512B but SSD drives often, as well as some newer magnetic drives, have larger block sizes.
For write performance it is as important to ensure that partition boundarys are block-size aligned as it is to use a file system with block/fragment sizes that are a multiple of (or the same as) the hardware block size. A mistake in this area will more than halve the sustained write speed of the drive. Unlike spinning drives the internal block size is often published by the SSD drive manufacturer.

Newer spinning magnetic media drives are beginning to be available with a (putative) 4K block size as well and partition alignment is also a factor with these drives.

Spindown is Bad

It's usually possible to configure laptop drives to not spin down. This should make for greater stability and more consistent response. Power consumption will increase, but still be very low. So it seems like a good configuration option for a low-power Soekris server. Applications that do not require regular disk access, e.g. routers and firewalls, may benefit less (but don't forget about logging).

FreeBSD provides the atacontrol(8) command. Syntax is 'atacontrol spindown $SECONDS $DRIVE' where DRIVE is either ad0 or ad1, and SECONDS is the idle delay. If SECONDS = 0, the drive will never spin down.

Heat

In warm environments, you may need to fit a small fan inside the case to keep the hard drive cool. High drive temperatures greatly increase the risk of drive failure. A fan running at even a low speed can greatly reduce temperatures. Drive temperature can often be monitored via SMART; smartmon is available on most open-source OS and supports temperature measurement on a wide range of drives. Note that Smartmon should not be set to perform automatic offline testing on a live server (so take care to override the default config file on the FreeBSD port of Smartmon): this is known to cause occasional ATA device driver timeouts in the FreeBSD kernel, and may reduce the useful life of the drive.

Particular drives

Solid State Drives

SSD drives can also be a good choice due to no moving parts, low power consumption, duty cycle, and low heat output. They are increasingly affordable.

SSD drives often have "block" sizes larger than the traditional 512B, usually 2 or 4K.

Hitachi Drives

Update (March 2009): In the UK, Dabs.com now stocks the Travelstar 5K320 EA (Extended Availability) drive: 320GB @5400 RPM. Hitachi part number HTE543232L9A300, Dabs part number 5H0QTS. Rated for 24*7 operation. (A 500 GB version has also been announced: if anyone finds these in stock somewhere, please update this page.)

Unlike laptop drives, these Hitachi drives do not keep spinning up and down when idle: they just keep spinning the whole time.